The invention relates to a method for transmitting data packets in a radio system and a corresponding communication device, a base station and the corresponding radio system.
For future “Enhanced UMTS Uplink” (E-DCH), a packet-oriented transmission with fast Hybrid ARQ (HARQ) is used, similar to that already standardized for HSDPA. In contrast to HSDPA, the “Enhanced UMTS Uplink” is, however, subject to the fast power control as described in Release 99, The emission power to be used for each channel (Release 99 and E-DCH) is specified by power offsets for the DPCCH (Dedicated Physical Control Channel, reference channel). The power offsets are communicated to the mobile station by signaling (higher layer signaling) or by a defined method from reference data. This ensures that each channel on average achieves the required target error rate.
If the mobile station exceeds its maximum permitted emission power during the fast power control, the transmission signal is scaled. As with the fast power control, this scaling operates on a “slot basis” and does not change the power ratio of the channels relative to the reference channel.
In Release 6, the transmission signal includes, in addition to one or more DPDCH(s) (Dedicated Physical Data Channel) and a DPCCH (Dedicated Physical Control Channel), also of one or more E-DPDCH(s) (Enhanced Dedicated Physical Data Channel). The slot-based scaling then effects an equivalent reduction in Release 6 of the total emission power at the terminal without changing the power ratio of the individual channels with respect to the DPCCH at the same time. The slot-based scaling is shown in FIG. 1. It takes place after the summing of the transmission signal.
Because in Release 6 the service quality of Release 99 DCH is prioritized compared with the service quality of the E-DCH channel, an E-DCH TTI based scaling that is performed at the start of the respective E-DCH TTIs is provided in addition to the slot-based scaling. Therefore, the following scaling process takes place in Release 6.
Scaling only of the E DCH channel (E-DCH TTI based) and scaling of the E DCH and DCH channels (slot based)
The main reason for the scaling is to prevent the mobile station disturbing the amplifier at the emission power limit, e.g. data transmission in the adjacent frequency bands, due to the non linearity. Possible causes for a power demand beyond the emission power limit are
Burst-type occurrence of a transmission overlap of channels with packet characteristics (e.g. simultaneous transmission of an HSDPA ACK/NACK and an E-DCH data packet)
Change of the data rate of one or more transport channels, especially a change of the data rate on the DCH channel
Deteriorating channel properties and thus increased requirement for emission power
As described above, the E-DCH is a packet channel. In the case of power scaling, the transmitted packet is transmitted at lower energy than the target energy, which increases the block error rate of this transmission compared with the target block error rate.
It has already been specified in UMTD Release 99 that if a mobile station threatens to exceed its maximum emission power the power of all channels is scaled, i.e. uniformly reduced. In a case where in Release 6 (E-DCH) a packet transmission has to be scaled because of the power limit of the mobile station, a procedure equivalent to Release 99 is used as described. Additionally, “E-DCH only TTI based” scaling was proposed for the E-DCH, which functions similarly to the R99 scaling, but in this case only scales the E-DCH signal. During the transmission of the E-DCH packets it was therefore previously necessary to take account of the disadvantage of the scaling and thus of an increased block error rate compared with the target block error rate. The missing energy of a transmission during scaling is also not taken into account in a retransmission and thus also leads to an increase in the error rate during the retransmission.
The generation of UMTS signals, the emission power of which is scaled by amplification factors, is described in specification 25.213 v6.1.0, section 4.2, Details of emission power control and especially the calculation of the amplification factors are described in specification 25.214 v6.1.0, section 5.
Based on this related art, it is one possible object to create a possibility of transmitting a high transmission quality at a satisfactory transmission quality.